std::basic_string<CharT,Traits,Allocator>::push_back
From cppreference.com
                    
                                        
                    < cpp | string | basic string
                    
                                                            
                    | void push_back( CharT ch ); | ||
Appends the given character ch to the end of the string.
Parameters
| ch | - | the character to append | 
Return value
(none)
Complexity
Amortized constant.
Exceptions
If an exception is thrown for any reason, this function has no effect (strong exception guarantee). (since C++11)
If the operation would result in size() > max_size(), throws std::length_error.
See also
| (C++11) | removes the last character (public member function) |